Bottom Line:
Females did not succeed in manipulating male effort using yolk androgens, since there was no relationship between the division of parental care within a pair and either original or foster egg androgen levels.The proportion of feeding visits by the male was higher when the male was old (55%) than when he was young (45%) and females laid eggs with higher androgen levels when mated with a young male.Young males did not exhibit any responses to yolk androgen levels either, which indicates that females cannot exploit their effort more than that of old males.

ABSTRACTFemale birds might be able to manipulate the parental effort of their male partner through elevated transfer of hormones to the eggs, since these hormones affect many chick traits that males might use as cues for adjusting the level of their investment. We experimentally studied whether female pied flycatchers Ficedula hypoleuca could manipulate male investment via yolk androgens. There is much more variation in yolk androgen levels between females than within clutches, and in order to change the androgen levels of the eggs, we swapped whole clutches between nests. To estimate the androgen levels of the clutch, we measured the androgen content of a single egg per clutch. Females did not succeed in manipulating male effort using yolk androgens, since there was no relationship between the division of parental care within a pair and either original or foster egg androgen levels. One of these relationships should have occurred if females were manipulating males. The proportion of feeding visits by the male was higher when the male was old (55%) than when he was young (45%) and females laid eggs with higher androgen levels when mated with a young male. Young males did not exhibit any responses to yolk androgen levels either, which indicates that females cannot exploit their effort more than that of old males. We suggest that females may allocate yolk androgens to adjust the growth trajectories of the chicks to poor growing conditions when mated with young males that are poor providers or occupying a poor territory.

Fig3: The proportion of feeding visits by the male in relation to (a) original yolk androgen levels in the nest (PC 1), and (b) foster yolk androgen levels in the nest (PC1)

Mentions:
The proportion of feeding visits by the male was not related to the yolk androgen levels of either the foster or original clutch (Table 2; Fig. 3). This indicates that females did not manipulate male investment via yolk androgens. The proportion of feeding visits by the male was, however, strongly influenced by male age: old males made on average 55%, and 1-year-old males only 45%, of feeding visits by the pair (Table 2; Fig. 4a). This was primarily due to females mated to 1-year-old males making more feeding visits than those mated to older males (F1,48 = 21.20, P < 0.0001, Fig. 4b). The difference in the feeding rates between 1-year-old and older males was not significant (F1,48 = 0.94, P = 0.33, Fig. 4c). There was no obvious difference in feeding rate between 1-year-old and older females (F1,48 = 1.87, P = 0.18, mean ± s.d.: 1-year-old: 13.89 ± 0.50, N = 10; older: 12.25 ± 1.32, N = 40). The total number of feeding visits per hour by the pair members was higher when the male was young (F1,48 = 5.47, P = 0.02; mean ± s.d.: 1-year-old: 28.07 ± 4.35; old: 25.20 ± 4.13). There were no significant interactions between original and foster yolk androgen levels or between either of these and male age (Table 2). The absolute feeding frequencies of neither male nor female parents were related to original or foster yolk androgen levels (all P > 0.5).Table 2

Fig3: The proportion of feeding visits by the male in relation to (a) original yolk androgen levels in the nest (PC 1), and (b) foster yolk androgen levels in the nest (PC1)

Mentions:
The proportion of feeding visits by the male was not related to the yolk androgen levels of either the foster or original clutch (Table 2; Fig. 3). This indicates that females did not manipulate male investment via yolk androgens. The proportion of feeding visits by the male was, however, strongly influenced by male age: old males made on average 55%, and 1-year-old males only 45%, of feeding visits by the pair (Table 2; Fig. 4a). This was primarily due to females mated to 1-year-old males making more feeding visits than those mated to older males (F1,48 = 21.20, P < 0.0001, Fig. 4b). The difference in the feeding rates between 1-year-old and older males was not significant (F1,48 = 0.94, P = 0.33, Fig. 4c). There was no obvious difference in feeding rate between 1-year-old and older females (F1,48 = 1.87, P = 0.18, mean ± s.d.: 1-year-old: 13.89 ± 0.50, N = 10; older: 12.25 ± 1.32, N = 40). The total number of feeding visits per hour by the pair members was higher when the male was young (F1,48 = 5.47, P = 0.02; mean ± s.d.: 1-year-old: 28.07 ± 4.35; old: 25.20 ± 4.13). There were no significant interactions between original and foster yolk androgen levels or between either of these and male age (Table 2). The absolute feeding frequencies of neither male nor female parents were related to original or foster yolk androgen levels (all P > 0.5).Table 2

Bottom Line:
Females did not succeed in manipulating male effort using yolk androgens, since there was no relationship between the division of parental care within a pair and either original or foster egg androgen levels.The proportion of feeding visits by the male was higher when the male was old (55%) than when he was young (45%) and females laid eggs with higher androgen levels when mated with a young male.Young males did not exhibit any responses to yolk androgen levels either, which indicates that females cannot exploit their effort more than that of old males.

ABSTRACTFemale birds might be able to manipulate the parental effort of their male partner through elevated transfer of hormones to the eggs, since these hormones affect many chick traits that males might use as cues for adjusting the level of their investment. We experimentally studied whether female pied flycatchers Ficedula hypoleuca could manipulate male investment via yolk androgens. There is much more variation in yolk androgen levels between females than within clutches, and in order to change the androgen levels of the eggs, we swapped whole clutches between nests. To estimate the androgen levels of the clutch, we measured the androgen content of a single egg per clutch. Females did not succeed in manipulating male effort using yolk androgens, since there was no relationship between the division of parental care within a pair and either original or foster egg androgen levels. One of these relationships should have occurred if females were manipulating males. The proportion of feeding visits by the male was higher when the male was old (55%) than when he was young (45%) and females laid eggs with higher androgen levels when mated with a young male. Young males did not exhibit any responses to yolk androgen levels either, which indicates that females cannot exploit their effort more than that of old males. We suggest that females may allocate yolk androgens to adjust the growth trajectories of the chicks to poor growing conditions when mated with young males that are poor providers or occupying a poor territory.